Question

我有一个MultiValueDictionary<string, string>，我试图按值获取密钥。

var dic = na.prevNext; // Getter to get MultiValueDictionary

string nodePointingToThisOne = "";
foreach (var item in dic)
{
    if(item.Value == "test")
    {
        nodePointingToThisOne = item.Key;
    }
    break;
}

这不起作用，所以我尝试了Linq：

string nodePointingToThisOne = dic.Where(x => x.Value == this.nodeID).Select(x => x.Key);

但两者都出现了这个错误：Operator '==' cannot be applied to operands of type 'System.Collections.Generic.IReadOnlyCollection<string>' and 'string'

所以我的问题是如何让这个比较适用于只读集合？我知道如果一个密钥存在多次我会遇到问题，但我暂时将问题减少到了这个问题。

我看了 Get Dictionary key by using the dictionary value

LINQ: Getting Keys for a given list of Values from Dictionary and vice versa

get dictionary key by value

Getting key of value of a generic Dictionary?

Get key from value - Dictionary<string, List<string>>

但他们处理的是“普通”字典。

Answer 1

由于{self}的Value属性可能包含多个值，因此无法使用==运算符直接将其与某些字符串进行比较。请改用Contains()：

.....
if (item.Value.Contains("test"))
{
    .....
}

...或方法链版本：

string nodePointingToThisOne = dic.Where(x => x.Value.Contains("test"))
                                  .Select(x => x.Key)
                                  .FirstOrDefault();

Answer 2

尝试按键进行迭代，然后比较值，并仅在值匹配时返回Key。

像这样：

foreach (var key in dic.Keys)
{
    if(dic[key].Contains("your value"))
        return key;
}

Answer 3

您可以迭代这样的键

   foreach (var key in dic.Keys)
    {
        if(key == "your key")
            return key;
    }

你也可以迭代这样的值

    foreach (var v in dic.Values)
    {
        if(v == "your value")
            return v;
    }

示例：

Dictionary<string, string> c = new Dictionary<string, string>(); c.Add("Pk", "Pakistan"); c.Add("Aus", "Australia"); c.Add("Ind", "India"); c.Add("Nz", "New Zeland"); c.Add("SA", "South Africa"); foreach (var v in c.Values) { if (v == "Australia") { Console.WriteLine("Your Value is = " + v); // perform your task } } foreach (var k in c.Keys) { if (k == "Aus") { // perform your task Console.WriteLine("Your Key is = " + k); } }

输出

你的价值是=＆＃34;澳大利亚＆＃34;
你的钥匙是=＆＃34; Aus＆＃34;

Answer 4

如果你看一下MultiValueDictionary,第81行会给你一个提示。它是：

 [TestInitialize]
 public void TestInitialize()
 {
     MultiValueDictionary = new MultiValueDictionary<TestKey, string>();
 }

 protected static void AssertAreEqual( IDictionary<TestKey, string[]> expected,
 IMultiValueDictionary<TestKey, string> actual )
 {
     Assert.AreEqual( expected.Count, actual.Count );
     foreach ( var k in expected.Keys )
     {
         var expectedValues = expected[ k ];
         var actualValues = actual[ k ];
         AssertAreEqual( expectedValues, actualValues );
     }
 }

因此，对于您的情况，解决方案类似：

foreach (var item in dic.keys)
{
    if(dict[item] == "test")
    {
        nodePointingToThisOne = item;
        return nodePointingToThisOne;
    }
}

Answer 5

为我工作：

foreach (int i in Dictionary.Keys)
{
   if (Dictionary.Values.ToString() == "Your Value")
   {
      return Dictionary.Keys;
   }
}

如何在IReadOnlyCollection <string>上比较键/值字典和==运算符？</string>

5 个答案: